Extraction of lignocellulosics for production of fibers and a precipitate-free hemicellulose extract

ABSTRACT

The present invention provides, among other things, methods including providing a biomass comprising lignin, associating the biomass with between 1-50 g/L formic acid at a temperature between 80° C. and 230° C. for at least 30 seconds to form an extraction liquor and an extraction solid, and separating at least a fraction of the extraction liquor from the extraction solid, wherein an amount of lignin equal to or less than 1.6% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patent application Ser. No. 61/761,880, filed on Feb. 7, 2013, and U.S. provisional patent application Ser. No. 61/878,975, filed Sep. 17, 2013, the disclosures of which are hereby incorporated by reference in their entirety.

BACKGROUND

The traditional paper industry located in temperate regions of the world is facing economic challenges due to a variety of factors including competition from new mills near forest plantations in tropical and subtropical regions. As such, the economic viability of traditional mills may be improved by, or even depend upon, the development of new and/or improved revenue sources. One avenue for developing new revenue sources is to leverage byproducts or waste products from traditional processes, or to improve upon the yield of existing processes.

SUMMARY

The present invention provides, among other things, methods of extracting lignocellulosics from a sample of biomass while preventing the formation of undesired precipitates, such as lignin precipitates. The present invention is based, in part, on the surprising discovery that the addition of between 1-50 g/L formic acid to a sample of biomass prior to, or substantially concurrently with, a hot water extraction of lignocellulosic compounds results in drastically reduced formation of certain precipitates, for example, lignin precipitates. In some embodiments, provided methods are also able to preserve one or more anhydrosugars in a substantially non-degraded state.

In some embodiments, the present invention provides methods including providing a biomass comprising lignin; associating the biomass with between 1-50 g/L formic acid at a temperature between 80° C. and 230° C. for at least 30 seconds to form an extraction liquor and an extraction solid; and separating at least a fraction of the extraction liquor from the extraction solid; wherein an amount of lignin equal to or less than 1.6% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C. In some embodiments, the formic acid is provided as a liquid or a gas. In some embodiments, the associating step further comprises associating the biomass with water. In some embodiments, the water is provided as a liquid or a gas. In some embodiments, at least one of the extraction liquor and extraction solid are cooled to below 100° C. prior to the separating step. In some embodiments, the extraction liquor is separated from the extraction solid at substantially the hydrolysis temperature and pressure.

In some embodiments, a biomass is also exposed to sulfuric acid during the associating step. In some embodiments, a biomass is associated with up to 5 g/L sulfuric acid. In some embodiments, a biomass is associated with between 1 and 2 g/L sulfuric acid, inclusive.

In some embodiments, provided methods further include washing the extraction solid by associating at least a portion of the extraction solid with water at a temperature between 80° C. and 230° C. for at least 30 seconds to form a wash liquor. In some embodiments, the water is provided as a liquid or a gas. In some embodiments, the washing step further comprises associating at least a portion of the extraction solid with between 1-50 g/L formic acid. In some embodiments, the formic acid is provided as a liquid or a gas. In some embodiments, the washing step occurs at between 100° C. and 230° C., inclusive. In some embodiments, the washing step occurs at between 150° C. to 170° C., inclusive. In some embodiments, the washing step occurs for between 30 seconds and 4 hours, inclusive.

According to various embodiments, provided methods may allow for improved recovery of one or more anhydrosugars as compared to previously existing methods including autohydrolysis. In some embodiments, the extraction liquor and wash liquor together comprise at least 7% of the anhydrosugars present in the biomass, based on the oven dry weight of the biomass.

Provided methods may provide extremely small amounts of lignin precipitation in the extraction liquor and/or wash liquor. In some embodiments, an amount of lignin equal to or less than 1.0% of the lignin present in the biomass precipitates in the wash liquor after cooling to below 100° C. In some embodiments, an amount of lignin equal to or less than 0.5% of the lignin present in the biomass precipitates in the wash liquor after cooling to below 100° C. In some embodiments, substantially no lignin precipitates in the wash liquor after cooling to below 100° C.

Any of a variety of types of biomass may be used according to various embodiments. In some embodiments, the biomass is selected from: wood chips, wood sawdust, wood residuals, agricultural cellulosic biomass, municipal solid waste, and mixtures thereof.

In some embodiments, the associating step occurs at a temperature between 100° C. and 230° C., inclusive. In some embodiments, the associating step occurs at a temperature between 150° C. to 170° C., inclusive. In some embodiments, the associating step occurs for between 30 seconds and 4 hours, inclusive.

In some embodiments, one or more of the extraction liquor and/or wash liquor are used in one or more subsequent processes. In some embodiments, at least a fraction of the extraction liquor and wash liquor are associated with each other.

As used in this application, the terms “about” and “approximately” are used as equivalents. Any numerals used in this application with or without about/approximately are meant to cover any normal fluctuation appreciated by one of skill in the relevant art. All literature citations are hereby incorporated by reference in their entirety, unless otherwise specified.

Other features, objects, and advantages of the present invention are apparent in the detailed description that follows. It should be understood, however, that the detailed description, while indicating embodiments of the present invention, is given by way of illustration only, not limitation. Various changes and modifications within the scope of the invention will become apparent to those skilled in the art from the detailed description.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is for illustration purposes only, not for limitation.

FIG. 1 shows exemplary results from application of provided methods on Southern hardwood chips, specifically, FIG. 1 shows, inter alia, the effect of 90 minutes formic acid extraction on formation of lignin precipitation products (LPPs) under various conditions: a) 5 g/L FA at 170° C., b) 5 g/L FA at 160° C., c) 10 g/L FA at 160° C.

FIG. 2 depicts a graph showing the cellulose to glucose yield from southern hardwood chips (SHM) that were subjected to provided methods (extracted groups labeled as “Ext.”), as compared to southern hardwood chip samples that were not subjected to provided methods (groups labeled as “original”). Samples were exposed to either 2.5 or 5 FPU/g of CTec2 (from Novozymes).

FIG. 3 depicts an exemplary sample of prehydrolyzed hardwood generated according to provided methods (including addition of 10 g/L formic acid during hot water extraction) as compared to a sample of prehydrolyzed hardwood prepared according to previously known methods.

FIG. 4 depicts an exemplary graph showing the percentage of monomeric sugars versus the concentration of sulfuric acid in the combined extract and wash liquor generated according to provided methods.

FIG. 5 depicts an exemplary graph of the amount of soluble (or UV) lignin and precipitated lignin in the combined extract and wash liquor generated versus the concentration of sulfuric acid concentration used in the 10 g/L formic acid association/extraction step.

DEFINITIONS

In order for the present invention to be more readily understood, certain terms are first defined below. Additional information for the following terms and other terms are set forth throughout the specification.

Approximately or about: As used herein, the term “approximately” or “about,” as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

Substantially: As used herein, the term “substantially” refers to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest. One of ordinary skill in the chemical arts will understand that biological and chemical phenomena rarely, if ever, go to completion and/or proceed to completeness or achieve or avoid an absolute result. The term “substantially” is therefore used herein to capture the potential lack of completeness inherent in many biological and chemical phenomena.

Other features, objects, and advantages of the present invention are apparent in the detailed description that follows. It should be understood, however, that the detailed description, while indicating embodiments of the present invention, is given by way of illustration only, not limitation. Various changes and modifications within the scope of the invention will become apparent to those skilled in the art from the detailed description.

DETAILED DESCRIPTION

The present invention provides, among other things, methods of extracting lignocellulosic materials from biomass, for example, woody biomass, without the formation of lignin precipitates. According to various embodiments, provided methods also allow for the extraction of one or more anhydrosugars that are substantially non-degraded.

Processing of Woody Biomass

The processing of biomass such as wood chips or other woody biomass has been occurring in various forms for centuries. For decades, improved methods of processing woody biomass have been a significant focus of development due to factors including new environmental regulations, the instability of oil prices, energy policies and simply overall global competitiveness. In recent years, the expansion of pulp and paper mills into so-called “biorefineries” has been a subject of considerable interest due, in part, to a significant decline in the demand for paper products and rising energy costs. The ability to process and separate previously unused or unusable byproducts from pulp refining is an attractive proposition for a pulp mill because it opens up new revenue streams.

In the case of woody biomass, there are three major components that can be converted into value added products: cellulose, hemicelluloses, and lignin. Cellulose is the most abundant carbohydrate biopolymer in the world and is made up of long, linear chains of about 10,000 glucose molecules linked end-to-end by 1-4 glycosidic bonds between D-glucopyranose units. Cellulose is the major chemical component of the fiber wall and contributes approximately 40-45% of the wood's dry weight. Cellulose tends to form intra and intermolecular hydrogen bonds that cause it to form both crystalline and amorphous regions in the plant cell wall. The crystalline regions cause cellulose to be relatively inert and insoluble in many solvents. The chemical structure of cellulose is depicted below:

Hemicelluloses are the second most prevalent component in woody biomass after cellulose. Hemicelluloses are amorphous heterogeneous polymers with degrees of polymerization between 100 and 200, and are sometimes acetylated. Hemicelluloses are generally made from five sugars: D-glucose, D-mannose, D-galactose, D-xylose, and L-arabinose. Less commonly, small amounts of L-rhamnose, 4-O-methyl-D-glucuronic acid, and D-galacturonic acid may be found in some hemicelluloses. In most cases, hemicelluloses are extensively branched, which the number and size of the branches depending upon the specific source of the biomass. The side chains tend to inhibit crystallization and therefore hemicelluloses are typically amorphous polymers. The irregular structure of the hemicellulose molecules minimizes the number of hydrogen bonds that can be formed between hemicellulose molecules and results in a less compact macro structure than that of cellulose.

Lignin is an amorphous aromatic polymer of phenyl propane units joined mostly by ether linkages or carbon-carbon bonds. While there is evidence of chemical bonding between lignin and carbohydrates, especially, hemicelluloses, the nature of this bonding is presently not fully understood. The aromatic rings in lignin contain one or two methoxy groups at the C-3 and/or C-5 positions, while the C-4 position is either a phenoxy ether or free phenolic group. The phenylpropane units are randomly cross-linked to each other by a variety of different chemical bonds. These linkages include both C—O—C(ether) and C—C(carbon carbon) linkages. The ether linkages represent two thirds or more of the total, while the rest are of the carbon to carbon type. These structural elements are not linked to each other in any particular order, although some of the linkage types seem to be more thermodynamically favored. It is commonly accepted that lignin is covalently bound to carbohydrates in woody biomass and this association has been termed the “lignin-carbohydrate complex (LCC).” An exemplary partial structure of a hardwood lignin molecule is below:

Processing of Woody Biomass—Pulping

The principal goal of chemical pulping is to dissolve lignin, leaving the carbohydrates mostly as cellulose for the production of paper and other specialty cellulose products. Typically, there are two main stages of chemical pulping: impregnation and cooking. In the impregnation stage chips are saturated with liquor which contains pulping chemicals. In this phase enough time must be allowed for the chemicals to diffuse equally to all parts of the chips before the delignification reactions start when the temperature is raised for cooking. During the cooking stage, the delignification reactions take place while the cooking chemicals are continuously supplied from the bulk of the solution to the reaction sites in the chips by diffusion through the wood capillary system. Delignification reactions may proceed under alkaline, acidic, or neutral conditions. However, the dominant pulping process is the alkaline kraft process.

Conventional Kraft Pulping

The conventional kraft cooking process is the most common chemical pulping process used in the world. This process uses an alkaline cooking white liquor (NaOH+Na₂S) to remove most of the lignin and part of the hemicelluloses found in woody biomass and produces a high quality, high strength pulp. The conventional kraft process has a number of advantages over previously used methods, with a major advantage being that the cooking chemicals can be economically recovered. Typically, the solubilized organics and spent cooking chemicals are separated as “black liquor” and, after concentration, the solids are burned, and a series of chemical reactions are used to restore the cooking liquor. The cooking process is typically conducted at elevated temperature and pressure. During the cooking process, approximately 40-50% of the woody biomass is dissolved and forms black liquor, which is a mixture of the dissolved wood solids and spent inorganic salts. The dissolved material consists primarily of degraded hemicelluloses, lignin and extractives, which are degradation products of the reactions in the processing equipment.

Residual spent cooking liquor typically contains the dissolved solids which are reaction products of lignin solubilization, sulphidation and degraded hemicellulose products. The liquor is often concentrated and burnt into a recovery boiler furnace to produce electricity and steam, while the inorganics leave the furnace as an inorganic smelt mostly containing Na₂CO₃ and Na₂S. After dissolution in water, this so-called “green liquor” is normally subjected to a causticization process which transforms Na₂CO₃ into NaOH, thereby regenerating white liquor.

Prehydrolysis Kraft (PHK) Process

The concept of pre-hydrolyzing woody biomass before applying a conventional pulping process has existed for many years. Generally, these methods have involved application of various acids, sulfite liquor, or autohydrolysis with hot water. Generally, these methods are intended to produce low-hemicellulose content dissolving pulps. However, because these methods dissolve hemicelluloses as a separate stream, value added products may be created if this stream were able to be generated in a form that is amenable to further processing of the hemicelluloses and other entities present in the extraction liquor.

Autohydrolysis (Hot Water Extraction)

One method that has been explored to extract hemicelluloses in a usable form from woody biomass is hot water extraction, also known as autohydrolysis. Autohydrolysis is an inexpensive and environmentally friendly way to selectively separate hemicelluloses from woody biomass prior to conventional pulping processes, such as Kraft pulping processes. Typically, autohydrolysis involves the exposure of woody biomass to water at a temperature between 150° C.-180° C. for a period of time. This exposure results in the formation of a crude hemicellulose extract, typically known as pre-hydrolysate liquor (also referred to herein as “extraction liquor”) and prehydrolyzed wood chips, which may be further kraft cooked to provide pulp.

While the use of autohydrolysis has several advantages, a primary disadvantage that has prevented widespread use of the process is the formation of lignin precipitates in the pre-hydrolysate/extraction liquor (also known as “sticky lignin”). It is thought that the precipitate forms because conventional autohydrolysis processes require removal of the pre-hydrolysate/extraction liquor from the processing machinery via mechanisms involving one or more of a drop in temperature and/or pressure, which allows for condensation/precipitation of the dissolved lignin. This precipitation results in scaling and clogging of the processing machinery and piping. While this problem is known to occur in conventional autohydrolysis processes, it has also been shown to occur in other prehydrolysis processes.

In an attempt to overcome the lignin precipitation issue, the Visbatch and VisCBC processes were developed. In each process, batch displacement technologies are used to displace the hot autohydrolysate via the use of hot alkaline liquor without allowing significant temperature and/or pressure drops during the process. However, because significant mixing occurs between the autohydrolysate and the displacing alkaline liquor, almost all of the dissolved sugars (e.g., hemicellulosic carbohydrate sugars) in the autohydrolysate are degraded. Other methods to prevent the formation of lignin precipitates in the pre-hydrolysate/extraction liquor typically use alkaline washes or other alkaline conditions, which leads to the same sugar degradation issue as in the Visbatch and VisCBC processes.

Avoidance of Sticky Lignin Problem Through Formic Acid-Based Extraction of Hemicelluloses

The present invention is based, in part, on the surprising discovery that application of formic acid to woody biomass, for example, during the extraction step of an autohydrolysis-type process, drastically reduces the amount of lignin precipitate (e.g., sticky lignin) found in the extraction liquor formed during the impregnation or other associating step. In some embodiments, application of formic acid substantially prevents the formation of lignin precipitates. The provided methods allow for significantly improved ability to process biomass and recover valuable components thereof. The decrease, or even prevention, of lignin precipitate formation opens up entirely new processing schemes and simplifies handling of process intermediates, for example, extraction liquors, as compared to previously available methods.

In some embodiments, the present invention provides methods including providing a biomass comprising lignin; associating the biomass with between 1-50 g/L formic acid at a temperature between 80° C. and 230° C. for at least 30 seconds to form an extraction liquor and an extraction solid; and separating at least a fraction of the extraction liquor from the extraction solid; wherein an amount of lignin equal to or less than 1.6% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C.

According to various embodiments, formic acid may be provided as either a liquid or a gas, as appropriate for a particular application of provided methods. In some embodiments, the associating step further comprises associating the biomass with water. In some embodiments, the water is provided as a liquid or a gas. Those of skill in the art will recognize whether a particular application of certain embodiments would benefit from the introduction of formic acid and, in some embodiments, water, as a gas or as a liquid.

The amount of formic acid provided will vary according to several factors including, but not limited to, the end product(s) desired, the biomass being processed, and/or the composition of the processing equipment used (e.g., 304C or 316C stainless steel). In some embodiments, between 1-50 g/L formic acid is provided. In some embodiments, formic acid is provided in a range between, 2-40 g/L, 2-35 g/L, 2-30 g/L, 2-25 g/L, 2-20 g/L, 3-25 g/L, 4-25 g/L, 5-20 g/L, or 5-15 g/L, inclusive of the end points of each range. In some embodiments, formic acid is provided in an amount equal to or greater than 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 g/L. In some embodiments, formic acid is provided in an amount equal to or less than 50, 45, 40, 35, 30, 25, 20, 15, or 10 g/L.

It is contemplated that a particular biomass may be associated with formic acid at any of a variety of temperatures. In some embodiments, a biomass is associated with formic acid at a temperature between 80° C. and 230° C., inclusive. In some embodiments, a biomass is associated with formic acid at a temperature between 80° C. and 225° C., 80° C. and 200° C., 90° C. and 200° C., 100° C. and 200° C., 100° C. and 190° C., 100° C. and 180° C., 100° C. and 170° C., 100° C. and 160° C., 100° C. and 230° C., or 150° C. and 170° C., inclusive of the end points of each range. In some embodiments, a biomass is associated with formic acid at a temperature equal to or greater than 80° C., 90° C., 100° C., 110° C., 120° C., 130° C., 140° C., 150° C., or 160° C. In some embodiments, a biomass is associated with formic acid at a temperature equal to or less than 230° C., 220° C., 210° C., 200° C., 190° C., 180° C., 170° C., or 160° C. In some embodiments, the temperature does not substantially change during the associating step. In some embodiments, the temperature does change during the associating step. In some embodiments, the temperature rises during the associating step. In some embodiments, the temperature drops during the associating step.

In addition to the amount of formic acid and the temperature at which a biomass is associated with formic acid, the amount of time during which a biomass is associated with formic acid may vary according to a specific embodiment. In some embodiments, a biomass is associated with formic acid for between 30 seconds and 4 hours. In some embodiments, a biomass is associated with formic acid for between 30 seconds and 3 hours, 30 seconds and 2 hours, 30 seconds and 1 hour, 1 minute to 4 hours, 1 minute to 3 hours, 1 minute to 2 hours, 1 minute to 1 hour, 1 minute to 50 minutes, 1 minute to 40 minutes, 1 minute to 30 minutes, 1 minute to 20 minutes, or 1 minute to 10 minutes. In some embodiments, a biomass is associated with formic acid for between 10 minutes and 2 hours, 20 minutes and 2 hours, 30 minutes and 2 hours, 40 minutes and 2 hours, 50 minutes and 2 hours, 1 hour and 2 hours, or 1 hour and 1.5 hours. In some embodiments, a biomass is associated with formic acid for at least 30 seconds, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 1 hour. In some embodiments, a biomass is associated with formic acid for at most 4 hours, 3 hours, 2 hours, or 1 hour.

It is specifically contemplated that one or more of: amount of formic acid, temperature during associating step, and/or time duration of associating step may depend upon a variety of factors, including the particle size of the biomass (e.g., lignocellulosic material) used in a particular embodiment.

In some embodiments, sulfuric acid (H₂SO₄) may also be associated with a biomass substantially concurrently with formic acid. In some embodiments, sulfuric acid and formic acid are provided sequentially, at a time prior to cooling of the extraction liquor and/or extraction solid to below 100° C. In some embodiments, a biomass is associated with formic acid, sulfuric acid, and water (each of which may be provided as a liquid and/or as a gas). In some embodiments, a biomass may be associated with up to 5 g/L sulfuric acid. In some embodiments, a biomass is associated with between 1 and 2 g/L sulfuric acid. Without wishing to be held to a particular theory, the addition of sulfuric acid to the associating step may serve to increase the conversion of certain sugar oligomers to monomers and decrease the percentage of lignin precipitate in the extract.

The association of a biomass and formic acid forms an extraction liquor and an extraction solid. In some embodiments, an extraction liquor comprises: hemicelluloses including hemicellulose carbohydrate sugars, such as anhydrosugars (xylose, mannose, glucose, arabinose, galactose and rhamnose) and sugar oligomers (xylan, mannan, glucan, arabinan, and galactan), acetic acid and acetyl groups linked to sugar units, methylglucuronic acid groups linked to sugar units, other uronic acid, cations (such as potassium, magnesium, etc), sugar degradation products (such as furfural and hydroxymethyl furfural, lactic acid, etc) and the majority of the lignin in the starting biomass. In some embodiments, an extraction solid comprises: cellulose, hemicelluloses, and the balance of the lignin from the starting biomass.

According to various embodiments, at least a fraction of the extraction liquor is separated from the extraction solid. The specific mechanism for achieving this separation may be accomplished by any application-appropriate means. For example, in some embodiments, at least a fraction of the extraction liquor is separated from the extraction solid via simple gravity displacement, decantation, centrifugation and filtration. Additionally, in some embodiments, at least a fraction of the extraction liquor is separated from the extraction solid via displacement with water (e.g., pressurized hot water). In some embodiments, a mixture of water and formic acid is used to displace at least a fraction of the extraction liquor from the extraction solid. The amount of formic acid used will vary according to a particular embodiment and any of the amounts or ranges disclosed herein may be appropriate for certain embodiments.

In some embodiments, it may be desirable or necessary to perform a plurality of separation/displacement steps. In some embodiments, such displacements (e.g., second or subsequent displacements) are referred to as “washes” or “washing”. In some embodiments, washing is accomplished by associating at least a portion of the extraction solid with water at a temperature between 80° C. and 230° C. for at least 30 seconds to form a wash liquor. According to various embodiments, the temperature at which the washing occurs and the length of time during which the washing occurs may be as described herein for the associating step(s).

In some embodiments, at least one of the extraction liquor and extraction solid are cooled to below 100° C. prior to the separating step.

One of the several advantages provided by various embodiments is that the extraction liquor does not exhibit significant lignin precipitation upon cooling and/or exposure to decreased pressures as compared to the associating step(s). In some embodiments, an amount of lignin equal to or less than 1.6% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C. In some embodiments, an amount of lignin equal to or less than 1.55%, 1.5%, 1.45%, 1.4%, 1.35%, 1.3%, 1.25%, 1.2%, 1.15%, 1.1%, 1.05%, 1.0%, 0.95%, 0.9%, 0.85%, 0.8%, 0.75%, 0.7%, 0.65%, 0.6%, 0.55%, 0.5%, 0.45%, 0.4%, 0.35%, 0.3%, 0.25%, 0.2%, 0.15%, 0.1% or 0.05% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C. In some embodiments, the amount of lignin present in the biomass is based on the oven dry weight of the biomass.

In some embodiments, the amount of lignin precipitate in the extraction liquor is quantified using the oven dry weight of the biomass. In some embodiments, when expressed in this way, an amount of lignin equal to or less than 0.45% of the lignin present in the biomass on an oven dry weight basis precipitates in the extraction liquor after cooling to below 100° C. In some embodiments, an amount of lignin equal to or less than 0.4%, 0.35%, 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, or 0.05% of the lignin present in the biomass on an oven dry weight basis precipitates in the extraction liquor after cooling to below 100° C.

According to various embodiments, a lignin precipitate may have varying levels of “stickiness,” sometimes referred to as either cohesion or adhesion. Without wishing to be held to a particular theory, it is herein contemplated that lignin precipitates with higher degrees of stickiness are more problematic from a processing standpoint and thus less desirable than “low stickiness” lignin precipitates. In some embodiments, the amount of lignin precipitates in an extraction liquor is the amount of moderate to high stickiness lignin precipitate.

Generally, according to various embodiments, a high “stickiness” precipitate has a particular combination of two characteristic properties: adhesion and cohesion. Without wishing to be held to a particular theory, it is contemplated that cohesion forces in a precipitate may provide physical bonding strength between the lignin polymer molecules in order to resist externally applied stresses, and adhesion forces tend to be stronger in situations characterized by low levels of viscosity, such as at an operating temperature leading to a larger contact area with a surface (i.e., an operating temperature significantly higher than the glass transition temperature of the substance). In some embodiments, cohesive forces may be determined and/or characterized by measuring one or more molecular parameters of the lignin, such as the weight average Mw, number average Mn and polydispersity or Mw/Mn. Thus, for a characterization of the degree of stickiness of the precipitate of any particular embodiment, one or more of: the T_(g), molecular weight distribution, and/or rheological behavior at the operating temperature range using Dynamic Mechanical Thermal Analysis (DMTA) of the precipitated lignin may be used. In some embodiments, one or more of the T_(g), molecular weight distribution, and/or rheological behavior at the operating temperature range using Dynamic Mechanical Thermal Analysis (DMTA) may be characterized and compared to tack measurement data in order to determine the degree of “stickiness” of a particular precipitate.

Another advantage provided by various embodiments is that a substantially improved proportion of the anhydrosugars present in the biomass may be recovered as compared to previously existing methods, such as simple autohydrolysis. In some embodiments approximately 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, or 13% of the anhydrosugars present in the biomass are recovered in the extraction liquor and/or wash liquor.

Any of a variety of types of biomass may be used according to various embodiments. In some embodiments, the biomass is selected from: wood chips, wood sawdust, wood residuals, agricultural cellulosic biomass, municipal solid waste, and mixtures thereof.

Exemplary Uses for Provided Extraction and/or Wash Liquors and/or Extraction Solids

The substantial decrease or prevention of the formation of lignin precipitates in an extraction and/or wash liquor generated, for example, during prehydrolysis of woody biomass prior to a kraft pulping process, allows for a variety of applications of the extraction and/or wash liquors. In addition, because a greater proportion of anhydrosugars, lignin and acetyl groups are removed using provided methods, the nature of the extraction solid is different than those generated by previously available methods. Accordingly, the extraction solids produced by provided methods may be particularly suitable for certain applications, including applications for which extraction solids would not have been suitable if generated via a previously known process (e.g., autohydrolysis).

One application for which provided extraction and/or wash liquors are suitable for in some embodiments is in the production of value-added chemicals such as acetic acid and biofuels. By way of specific example, extraction of hemicelluloses into usable form allows for their use as a feedstock for the production of, for example, xylitol, barrier films, ethanol, jet and diesel fuel, gasoline, furfural, formic and acetic acid, butanol, acrylic acid, adipic acid, acetone, isopropanol, polypropylene, and lactic acid.

In addition, the extraction solids produced by provided methods are particularly suitable for certain applications. For example, in some embodiments, provided extraction solids are useful in the production of wood-reinforced composites such as those used in home construction materials, car fenders, bridge girders, skateboards, to name a few. In some embodiments, extraction solids are dried to make wood meal, which is then blended with a polymer (e.g., polypropylene) and additives such as methylacetylene-propadiene propane (MAPP) to form a feedstock for one or more products.

Another example of potential uses of extraction solids produced by provided methods is in the production of value added-chemical and biofuels. In some embodiments, provided extraction solids are enzymatically hydrolyzed to form a glucose solution which is used in one or more methods for producing chemicals, for example butanol, lactic acid, acrylic acid, adipic acid, acetone, isopropanol, ethylene, and propylene, or certain biofuels.

EXAMPLES Example 1 Formic Acid-Assisted Water Extraction of a Mixture of Southern Hardwood Chips Followed by Enzymatic Hydrolysis of the Extracted Wood

Extraction of a mixture of southern hardwood chips (SHM) was conducted in a Modified Dionex ASE100 apparatus. The ASE100 and its modification have been described (see Tunc et al., 2008, Hemicelluloses Extraction of Mixed Southern Hardwood with Water at 150° C.: Effect of Time, Industrial Engineering Chemistry Research, 47(18): 7031-7037). SHM contains sweet and black gum (35%), oak (35%), maple (15%), poplar and sycamore (12%) and southern magnolia (3%). The chemical composition of SHM is summarized in Table 1. The average wood chip dimensions are: 31 mm long, 14 mm wide and 4 mm thick. The moisture content of SHM chips used for the experiments is around 6%.

TABLE 1 Chemical composition of Southern hardwood mixture Component % by wt. Component % by wt. Arabinan 0.51 ± 0.01 AcG 3.23 ± 0.05 Galactan 1.00 ± 0.01 UAG 4.36 ± 0.10 Glucan 42.80 ± 0.61  Lignin 28.03 ± 0.19  Xylan 15.17 ± 0.03  Extractives 2.00 ± 0.11 Mannan 2.13 ± 0.05 Ash 0.38 ± 0.08 AcG: Acetyl groups UAG: Uronic acid groups

About 20 g of a SHM were associated/contacted with 10 g/L aqueous formic acid in the 100 ml of Dionex ASE100 extraction cell. The cell was filled completely at 150 atm pressure with an aqueous solution of FA (about 90 ml) leading to a liquid to wood ratio (L/W) in the extraction cell of about 4.5 L/Kg. The temperature of the cell was quickly raised to 160° C. and kept at this temperature for 90 minutes. Then the liquid (i.e., extraction liquor) in the cell was displaced using about 150 mL of 10 g/L aqueous formic acid at 160° C. Thus the total L/W ratio of the aqueous FA solution fed relative to the dry original wood solids is about 13 L/kg. The displacement step was immediately followed by a 5 minute nitrogen gas purge at 160° C. to remove most of the free liquid in the extraction cell and piping.

About 200 ml of liquid is obtained in the collection bottle because about 40 ml of the fresh formic acid solution remains in the extracted wood. The monomer and total sugar concentrations in the liquid were determined by HPAEC-PAD analysis by direct injection of a sample and by injection after 1 h hydrolysis of the sample with 4% H₂SO₄ at 121° C. in an autoclave respectively. The lignin content of each extract was determined using UV analysis at 205 nm because the UV absorption of sugar degradation products such as furfural and hydroxymethylfurfural (HMF) is minimal at 205 nm. Acetic acid, furfural and HMF in the liquid phases were also determined by HPLC. The increase in formic acid concentration measured by HPLC was too small relative to the amount of formic acid charged in the FA extract. However the amount of formic acid formed may be estimated based on the finding that the amount of formic acid released during water hydrolysis is about 20% (w/w) of that of acetic acid released. So the amount of formic acid released is expected to be about 0.5% based on wood. At the present conditions this would increase the formic acid concentration in the FA extract by about 0.4 g/L, which is small compared to the feed FA concentration of 10 g/L.

The extracted wood yield was 77.6%, i.e. a removal of 22.4% on original oven dry wood. Most of the dissolved components were determined by the above described analysis methods giving a total removal weight of 19.4% as 9.6% xylan (from total xylose), 1.2% glucan, 0.9% mannan, 0.8% galactan, 0.5% arabinan, 3% lignin, 3% acetyl groups (from acetic acid) and 0.4% furfural, all based on o.d. original wood. The concentration of sugars in the form of oligomers as xylan, mannan and glucan is about equal to that of the monomers as xylose, mannose and glucose, respectively.

It is visually observed that LPPs are generated during extraction with 5 g/L of FA for 90 minutes at higher temperatures (170 C) (see FIG. 1 a) just as was found during extraction with pure water at temperatures of 150 to 200° C. (see Gutsch et al. 2012, Comparative evaluation of autohydrolysis and acid-catalyzed hydrolysis of Eucalyptus globulus wood, Bioresource Technology, 109: 77-85). In Gutsch et al., it is reported that on average a precipitate amount of about 1.0% on original wood is formed, with values ranging from 0.2 to 1.7%. The amount of the LPPs formed in trial 1 as shown in FIG. 1 a was not determined, but its lignin nature was verified by UV analysis and the fact that they dissolve in 94% dioxane-water. The temperature was then lowered to 160° C. in trial 2. The picture of the extract produced in trial 2 (FIG. 1 b) shows that no LPPs are generated after extraction with 5 g/L FA and 160° C. for 90 minutes. When the FA concentration was increased from 5 to 10 g/L in trial 3 it can be seen in FIG. 1 c that no LPPs are formed when SHM is extracted at 10 g/L FA and 160° C. for 90 minutes.

The original SHM chips and those extracted with 10 g/L FA at 160° C. for 90 min were subjected to enzymatic saccharification at commercial enzyme dosages of 2.5 and 5 FPU/g cellulose after milling to 1 mm. The cellulose to glucose conversion yield obtained in these four experiments is shown in FIG. 2. As expected the enzymatic saccharification of the original SHM is minimal due to the “recalcitrance” of untreated wood. The maximum cellulose conversion yield of the original SHM reaches about 18% at a charge of 5 FPU/g cellulose after 120 h. However FIG. 2 also shows that the cellulose conversion yield is dramatically enhanced after 10 g/L FA pretreatment, and reaches about 82% after 72 hours at a low enzyme dosage of 5 FPU/g cellulose.

The composition of the original and 10 g/L FA extracted wood in terms of the three major components (cellulose, hemicellulose and lignin) as well as the acetyl group content (AcG) is given in Table 2. Also listed in Table 2 is the cellulose to glucose conversion yield at 5 FPU/g cellulose after 48 hours of enzymatic hydrolysis. It shows that the cellulose conversion yield increases dramatically with decreasing hemicellulose and especially acetyl groups content. It is well known that hemicelluloses can decrease the digestibility of cellulose by hindering the accessibility of enzymes on to cellulose (see Mussatto et al., 2008, Effect of hemicelluloses and lignin on enzymatic hydrolysis of cellulose from brewer's spent grain, Enzyme Microb. Tech., 43: 124-129). The low acetyl group content of the solids also likely contributes to the improved digestibility as was recently documented (see Chen et al., 2012, The impacts of deacetylation prior to dilute acid pretreatment on the bioethanol process, Biotechnology for Biofuels, 5(8): 2-14). Deacetylation of the hemicelluloses leads to pore opening of the cell wall, as has been shown by Inalbon et al., which increases the enzyme accessibility (see Inalbon et al., 2009, The deacetylation reaction in Eucalyptus wood: kinetics and effects on the effective diffusion, Bioresource Technology, 100(7): 2254-2258).

TABLE 2 Composition of original wood and formic acid extracted wood as well as glucose converstion of cellulose at 5 FPU/g cellulose after 48 hours. Glucose g/100 g od sample Conversion Sample Lig. Cell. Hemi. AcG yield, % Original SHM 28 42 29 3.3 11 Ext. Wood (10 g/L FA) 31 56 13 0.7 74

This example shows that association/extraction of southern mixed hardwood chips with 10 g/L formic acid (FA) at 160° C. for 90 min leads to 12.4% carbohydrate and 3.0% lignin dissolution (all % on original wood basis) without significant formation of lignin precipitates in the extract. The cellulose to glucose yield of the FA treated wood at a commercial enzyme charge of 5 FPU/g cellulose is 74% after 48 h compared to only 11% for the original wood chips. An almost equal amount of monomeric and oligomeric sugars are present in the formic acid extract.

Example 2 Formic Acid-Assisted Water Extraction of a Mixture of Northeastern Hardwood Chips Without Formation of “Sticky Lignin” in the Extraction Liquor Followed by Kraft Pulping to Form a Prehydrolysis-Kraft Pulp Feedstock for Dissolving Pulp and Specialty Cellulose

In this example commercial “green” mixed Northeastern hardwood chips (NEHM) were screened to chip length and thickness of ⅝- 9/8 and 0.20-0.47 inches, respectively. The NEHM chips contain maple (58.1%), birch (36.0%) and beech (5.1%) and trace amounts of softwood. The moisture content of the wood particles was about 34.6% on a wet basis. The chemical composition of the chips on o.d. basis is shown in Table 3.

TABLE 3 Chemical Composition of Northeastern Hardwood Mixture Component % by wt. Component % by wt. Arabinan 0.47 ± 0.01 AcG 5.49 ± 0.28 Galactan 1.02 ± 0.02 UAG 5.97 ± 0.40 Glucan 37.98 ± 0.66  Lignin 27.52 ± 0.11  Xylan 16.42 ± 0.10  Ash 0.22 ± 0.11 Mannan 1.70 ± 0.05 AcG = acetyl groups, UAG = uronic acid groups

The hot water association/extraction and chip washing tests were carried out in high-pressure bombs (each having a volume of 220 mL) which can rotate back and forward in a temperature controlled polyethylene-glycol (PEG 400, Baker) bath. For each test 40 grams of fresh wood chips were placed in a bomb. Hot water extraction of the NEHM was performed using 77.8 mL of a 10 g/L formic acid (FA) solution (room temperature pH 2.3) so that the total liquor to wood ratio including the original moisture in the wood was equal to 3.5 L/kg. For comparison the extraction was also performed with pure deionized water at otherwise the same conditions as the formic acid reinforced extraction. This represented the autohydrolysis control test.

Association/extraction in the preheated bath was performed for 100 minutes which includes about 10 minutes to heat the bombs with content to 160° C. Then the bombs were immersed in ice-water and opened after 10 minutes. The extraction liquor and extracted wood chips were transferred into a 200 mesh nylon bag to collect the extract by drainage. The extraction liquor was quantified (42-44 ml) and saved for further analysis while the extracted wood was returned to the bomb for further water washing. The same volume (42-44 ml) of deionized water (i.e. the same volume as that of the collected prehydrolysate) was charged into the bombs and the bombs were returned to the oil bath for a further 70 min of washing at 160° C. Then the bombs were again cooled in ice-water and the content was transferred into a nylon filtering bag to drain the wash liquor. The amount of drained wash water collected is about 31-33 ml. The association/extraction and subsequent chip washing conditions are summarized in Table 4. All experiments were performed in duplicate.

TABLE 4 Extraction and Washing Experimental Conditions Process Step Process Conditions Extraction Extractant: 10 g/L Formic acid aqueous solution L/W ratio: 3.5 L/kg Extraction temperature: 160° C. Extraction time: 100 min (includes heat-up time of about 10 minutes) Washing Extraction Solvent: Deionized Water L/W ratio: 3.5 L/kg Washing temperature: 160° C. Washing time: 70 min (includes heat-up period of about 10 minutes)

The solid yields of the extracted and water washed wood are 81.4 and 82.7% for FA pre-extraction and autohydrolysis, respectively. The concentrations of the dissolved sugars, lignin and other components in the drained extract during 10 g/L FA extraction and hot water extraction (autohydrolysis) are given in Table 5. Also included are their volumes (as L/W ratio) and pH values. In both the FA and hot water extract liquids, the xylan concentration is significantly higher than the other components. Lignin and acetic acid are the next highest concentrations. It can also be seen that the volume of the drained extract represents about 48% of the original liquid in contact with the chips during FA treatment or autohydrolysis (1.7 L/W of original L/W ratio of 3.5 L/kg). The washing step produces another 1.5 L/kg original wood. As expected the measured total organics concentration in the wash liquor is about half of that in the corresponding pre-hydrolysate or autohydrolysate liquor ((3.5-1.7)/3.5)=0.5). Thus the combined drained extract and wash water contain about 70% of the wood dissolved during the pre-extraction or autohydrolysis treatment ((100×1.7+50×1.5)/3.5=70). It can be seen that the pH values of the drained liquors are slightly lower for FA pre-hydrolysis than that of autohydrolysis. Finally it can be calculated that the formic acid charge on wood is 10×2.94×1000/100=2.94 g/100 g wood or 3%.

TABLE 5 Volumes and pH's of the drained extracts and washing liquids and the concentration of the major components in these liquids in [g/L] for FA extraction and autohydrolysis 10 g/L FA Extraction Hot Water Extraction (Prehydrolysis) (Autohydrolysis) Prehydrolysis Washing Autohydrolysis Washing Liquid Added 2.9 1.7 2.9 1.7 (L/kg) Wood Moisture 0.6 1.8 0.6 1.8 (L/kg) Total 3.5 3.5 3.5 3.5 (L/kg) Drained 1.7 1.5 1.7 1.6 (L/kg) pH 2.6 2.8 2.7 2.8 Component g/L g/L g/L g/L Arabinan 0.9 0.5 0.6 0.6 Galactan 1.9 1.2 1.3 0.7 Glucan 4.6 1.3 3.5 1.2 xylan 20.9 13.3 17.4 9.4 Mannan 2.4 0.70 2.1 1.3 Total 31 17.0 25.0 13.0 anhydrosugars Lignin 10.5 2.7 9.1 2.4 HAc 10.5 5.3 10.1 3.3 Total 51.70 25.3 44.0 21.5

Table 6 shows the amounts of sugars, lignin and acetyl groups removed, expressed as weight percentage of the original dry NEHM chips for prehydrolysis and washing for both 10 g/L FA and hot water extraction (i.e. autohydrolysis). It can be seen that the percentage removal of all components is generally higher in the case of FA prehydrolysis than that of autohydrolysis for both the extract and wash liquid. The total amount of anhydrosugars removed with the drained extract and wash liquor are 7.7 and 6.1% based on original wood weight for FA pre-extraction and autohydrolysis respectively. Xylan and lignin are the major wood polymers contributing to the total liquid extraction yield.

TABLE 6 Removal of anhydrosugars, lignin and acetyl groups (ACG) from NEHM chips during FA pre-extraction and autohydrolysis in g/100 g original wood 10 g/L FA Pre-extraction Hot water Extraction Drained or Autohydrolysis Pre- Drained Drained Drained Extract Washing Autohy- Washing Liquid Liquid drolysate Liquid [g/100 g [g/100 g [g[100 g [g/100 g Component of o.d wood] of o.d wood] of o.d wood] of o.d wood] Arabinan 0.16 0.08 0.18 0.09 Galactan 0.32 0.18 0.21 0.09 Glucan 0.77 0.19 0.58 0.18 Xylan 3.5 2.02 2.89 1.4 Mannan 0.4 0.10 0.35 0.09 Total 5.1 2.6 4.2 1.9 anhydrosugars Lignin 1.8 0.4 1.5 0.37 HAc 1.8 0.8 1.7 0.50 Total 8.7 3.8 6.8 2.7

The hemicelluloses are extracted from hardwood chips in the form of monomer sugars and liquid-soluble oligosaccharides with various degrees of polymerization. The oligosaccharides can be further hydrolyzed to monosacharides by using acids or enzymes. Hydrolysis in 4% sulfuric acid at 121° C. for one hour was used to hydrolyze all oligomer sugars into monomer sugars. The amount of oligo-sugars was calculated by difference of the total sugar content after sulfuric acid hydrolysis and the amount of monomeric sugars in the original filtrate. The chemical composition of the FA extract and autohydrolysate in terms of monomeric and oligomeric sugars expressed in g/100 g original wood is given in Table 7.

TABLE 7 Monomeric and oligomeric sugars in extract and washing drain liquids Hot water Extraction or 10 g/L FA Pre-extraction (drained Autohydrolysis (drained pre-extract plus wash liquid) autohydrolysate plus wash liquid) Oligomers Monomers Oligomers Monomers [g/100 g of [g/100 g of % of [g/100 g of [g/100 g of % of Component o.d wood] o.d wood] Monomers o.d wood] o.d wood] Monomers Arabinan 0.13 0.10 44 0.16 0.11 41 Galactan 0.28 0.22 44 0.20 0.10 33 Glucan 0.63 0.33 34 0.60 0.16 21 Xylan 3.58 1.93 35 3.11 1.20 28 Mannan 0.36 0.14 28 0.35 0.09 21 All sugars 4.98 2.72 4.42 1.66

It can be seen that in the drained FA plus wash extract the xylan monomer amount is 1.93 g/100 g wood while the xylo-oligomers represent 3.58 g/100 g giving a total of 5.51 g/100 g. Thus 35% of the dissolved xylan in the collected liquid is in the form of xylose. Similarly, for the case of autohydrolysis the xylose and xylo-oligomers are 1.20 g/100 g and 3.11 g/100 g, respectively, giving 28% in monomeric form. The monomer percentages are highest for arabinan and galactan and lowest for mannan. The monomer percentages of all sugars are 35% and 27% in the combined drained FA and autohydrolysis liquids, respectively. Thus the FA pre-extraction process yields a greater amount of sugar hydrolysis both in terms of total sugar dissolution and monomeric fraction. This is expected based on the slightly lower pH of the FA extract compared to that of autohydrolysis (see Table 5).

During pre-extraction of hardwood with hot water the pH of the extraction liquor becomes acidic due to release of acetic acid. Under acidic conditions at high temperature carbonium ions are formed as part of the cleavage of α and β-aryl ether bond of lignin. Without wishing to be held to a particular theory, it is likely that these carbonium ions on dissolved lignin may react with other dissolved lignin fragments leading to the formation of higher molecular weight lignin. This lignin precipitates onto the surface of the fibers and increases the amount of residual lignin (by resisting delignification) in the final pulp product (see Li and Gellerstedt, 2008, Improved lignin properties and reactivity by modifications in the autohydrolysis process of Aspen wood, Industrial crops & products, 27(2): 175-181). The lignin also precipitates on the surface of process equipment. Formation of lignin precipitation products (LPPs) have been observed during hot water extraction (i.e. autohydrolysis) of hardwood chips when the temperature of the extract is lowered (see Gutsch et al., 2012). Gutsch et al. reported that at wood extraction yields of about 85% to about 70% the formation of LPPs varies from about 1.1 to 1.7% based on the original dry wood weight. These yields were obtained by autohydrolysis at 150° C. for more than 70 minutes and at 170° C. for 18 to 60 minutes. Because the sticky lignin precipitates lead to troublesome operation, a practical approach which avoids the formation of these insoluble components during autohydrolysis is a prerequisite for commercialization of water autohydrolysis of wood chips. This is achieved by various embodiments of the present invention, as shown in this Example with the presence of 10 g/L formic acid in the water hydrolysis step. FIG. 3 shows that the drained 10 g/L FA prehydrolysate is a transparent solution while the drained autohydrolysate generated in this study has a significant amount of a dark lignin precipitate at the bottom of the test tube. Thus it appears that the presence of 10 g/L FA during wood hydrolysis avoids the formation of lignin precipitates.

The 10 g/L FA pre-extracted and washed wood chips were subsequently Kraft pulped at 14% effective alkali (EA) (charge as g Na₂O/100 g od wood), a sulfidity of 41% and a causticizing efficiency of 38%. First the extracted chips were impregnated at a L/W of 3.5 L/kg for 60 min at 115° C. followed by cooking at 160° C. for 60 minutes. Conventional Kraft pulps were also produced by impregnation (T=115° C. and t=60 min) and Kraft control cooking (T=160° C. and t=120 min) of the NEHM chips at the same EA charge of 14% and L/W of 3.5 L/kg. It should be noted that the actual cooking time for the conventional Kraft cooks was twice that of the pre-hydrolysis Kraft cooks.

The pulp yield of the FA pre-extraction Kraft pulp was 35.5% (based on original oven dry wood) and the kappa number was 13.2 while the residual effective alkali (REA) was 11.5 g Na₂O/L. The corresponding values for the conventional Kraft pulp were a pulp yield of 57.5% at a kappa number of 23.5 and REA of 7.8 g/L. The intrinsic viscosities of the two pulps were 922 and 958 cm³/g respectively. The pulp yield of the FA pre-hydrolysis Kraft pulp was slightly lower than 38% which has been reported for hardwood pre-hydrolysis Kraft (see Mateos-Espejel et al 2013, Implication of Converting a Kraft pulp mill to a dissolving pulp operation with hemicellulose extraction stage, Tappi Journal, 12(2): 29-38). Sugar analysis of the FA pre-hydrolysis Kraft pulp showed that besides cellulose the pulp only contained 2% hemicellulose, which is well below the level of 3% reported as typical for pre-hydrolysis Kraft dissolving pulp. The low hemicellulose content in the present FA pre-hydrolysis Kraft pulp also explains the relatively low overall pulp yield. For comparison, the conventional Kraft pulp contains 14% hemicelluloses.

Example 3 Effect of Varying Levels of Formic Acid on Formic Acid-Assisted Water Extraction of a Mixture of Northeastern Hardwood Chips Without Formation of “Sticky Lignin” in the Extraction Liquor

Another set of formic acid treatment experiments on the NEHM wood chips was performed using the same procedures as described in example 2 at 10 g/L formic acid, but now performed at different formic acid concentrations (0, 5, 10 and 15 g/L). The concentrations in g/L were determined in the extract of the precipitate and that of soluble (or UV) lignin. The amount of extract collected in these series of experiments in terms of L/W ratio was 2.35 L/kg oven dry wood in each case. As shown in Table 8, the concentration of the precipitate in the extract decreases from 2.9 g/L to 1.5 g/L when the formic acid concentration is increased from 0 to 15 g/L, while that of the soluble lignin determined by UV spectroscopy increases from 5.6 g/L to 6.4 g/L. However, the sum of these two lignin concentrations listed in Table 8 as “All lignin” does not change appreciably with increasing formic acid concentration. Therefore these results show that increasing formic acid concentration during extraction reduces the formation of lignin precipitate from the soluble lignin in the extract.

TABLE 8 Lignin concentration in drained extract liquor in the form of precipitate and as soluble lignin at different formic acid concentrations during extraction. L/W ratio of drained extracts is 2.35 L/kg od wood. 0 g/L 5 g/L 10 g/L 15 g/L Lignin Formic Formic Formic Formic concentration Acid acid Acid Acid in extract extraction extraction extraction extraction As precipitate 2.9 2.6 2.4 1.5 (g/L) As soluble 5.6 5.7 6.1 6.4 lignin (g/L) All lignin 8.5 8.3 8.5 7.9 (g/L)

Example 4 Formic acid and sulfuric acid assisted water extraction of a mixture of Northeastern hardwood chips without formation of “sticky lignin” and increased hydrolysis of the dissolved sugars to monomers in the extract

In this example the same Northeastern hardwood chips (NEHM) were used as described in Example 2 (see Table 3). The chips were also exactly treated in the same was a described in Example 2, except that in addition to 10 g/L of formic acid different amounts of sulfuric acid were also included in the associating/prehydrolysis step. Thus the objective was to test whether the sugars extracted from the wood could be further hydrolyzed to monomers during the FA treatment step while maintaining or preferably decreasing the amount of the precipitated lignin. The sulfuric acid concentrations in the 10 g/L FA solutions added to the NEHM at L/W ratio of 3.5 L/kg were: 0.0, 0.25, 0.50 and 1.0 g/L. It can be seen in FIG. 4 that the percentage of monomeric to total sugars increases from about 35% without sulfuric acid to about 85% at 1 g/l of H₂SO₄.

This Example shows that provided methods are able to generate significant quantities of monomeric sugars, particularly when sulfuric acid is administered with FA. Furthermore, in this Example, the amount of lignin precipitate was quantified in the separated (i.e., collected by drainage) extract and wash liquor, and expressed in % on oven dry NEHM. The procedure of association/extraction and washing is as was described in Example 2. The quantity of drained extract and wash liquor in these 4 experiments expressed in terms of Liquor-to-Wood (L/W) ratio are 1.7 and 1.6 L/kg od wood, respectively. The percentage of precipitated lignin in the four experiments are listed in Table 9:

TABLE 9 Quantification of Lignin Precipitate Precipitate 10 g/L FA + 10 g/L FA + 10 g/L FA + (g/100 g 0.25 g/L 0.5 g/L 1.0 g/L od wood) 10 g/L FA H₂SO₄ H₂SO₄ H₂SO₄ Extract 0.36 0.30 0.26 0.19 liquor Wash 0.10 0.11 0.10 0.08 liquor Combined 0.46 0.41 0.36 0.27 liquor

Table 9 shows that the amount of lignin precipitate in the extract decreases with increasing sulfuric acid concentration, while the amount of precipitate in the ash liquor is a few times lower and relatively unchanged. The amount of precipitate in the combined extract and wash liquor is plotted in FIG. 5. Also included in this figure is the amount of dissolved lignin in the combined extract and wash liquor which shows that the dissolved lignin (UV lignin) increases with increasing sulfuric acid concentration. Interestingly, the total amount of lignin in soluble form and as precipitate in the combined extract and wash liquor sum up to a constant value of about 1.2 g/100 g oven dried NEHM. Therefore, this Example shows that the addition of sulfuric acid to the 10 g/L FA treatment reduces the lignin precipitate formation from the soluble lignin in the extract.

EQUIVALENTS AND SCOPE

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. The scope of the present invention is not intended to be limited to the above Description, but rather is set forth in the following claims: 

1. A method comprising providing a biomass comprising lignin; associating the biomass with between 1-50 g/L formic acid at a temperature between 80° C. and 230° C. for at least 30 seconds to form an extraction liquor and an extraction solid; and separating at least a fraction of the extraction liquor from the extraction solid; wherein an amount of lignin equal to or less than 1.6% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C.
 2. The method of claim 1, wherein the formic acid is provided as a liquid or a gas.
 3. The method of claim 1, wherein the associating step further comprises associating the biomass with water.
 4. The method of claim 3, wherein the water is provided as a liquid or a gas.
 5. The method of claim 1, further comprising washing said extraction solid by associating at least a portion of the extraction solid with water at a temperature between 80° C. and 230° C. for at least 30 seconds to form a wash liquor.
 6. The method of claim 5, wherein the water is provided as a liquid or a gas.
 7. The method of claim 5, wherein the washing step further comprises associating at least a portion of the extraction solid with between 1-50 g/L formic acid.
 8. The method of claim 7, wherein the formic acid is provided as a liquid or a gas.
 9. The method of claim 5, wherein the extraction liquor and wash liquor together comprise at least 7% of the anhydrosugars present in the biomass, based on the oven dry weight of the biomass.
 10. The method of claim 5, wherein the washing step occurs at between 100° C. and 230° C., inclusive.
 11. The method of claim 5, wherein the washing step occurs at between 150° C. to 170° C., inclusive.
 12. The method of claim 5, wherein the washing step occurs for between 30 seconds and 4 hours, inclusive.
 13. The method of claim 5, wherein an amount of lignin equal to or less than 1.0% of the lignin present in the biomass precipitates in the wash liquor after cooling to below 100° C.
 14. The method of claim 5, wherein an amount of lignin equal to or less than 0.5% of the lignin present in the biomass precipitates in the wash liquor after cooling to below 100° C.
 15. The method of claim 1, wherein the biomass is selected from: wood chips, wood sawdust, wood residuals, agricultural cellulosic biomass, municipal solid waste, and mixtures thereof.
 16. The method of claim 1, wherein the associating step occurs at a temperature between 100° C. and 230° C., inclusive.
 17. The method of claim 1, wherein the associating step occurs at a temperature between 150° C. to 170° C., inclusive.
 18. The method of claim 1, wherein the associating step occurs for between 30 seconds and 4 hours, inclusive.
 19. The method of claim 1, wherein an amount of lignin equal to or less than 1.0% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C.
 20. The method of claim 1, wherein an amount of lignin equal to or less than 0.5% of the lignin present in the biomass precipitates in the extraction liquor after cooling to below 100° C.
 21. The method of claim 5, wherein at least a fraction of the extraction liquor and wash liquor are associated with each other.
 22. The method of claim 1, wherein at least one of the extraction liquor and extraction solid are cooled to below 100° C. prior to the separating step.
 23. The method of claim 1, wherein the associating step further comprises associating the biomass with sulfuric acid.
 24. The method of claim 23, wherein the biomass is associated with up to 5 g/L sulfuric acid.
 25. The method of claim 23, wherein the biomass is associated with between 1 and 2 g/L sulfuric acid, inclusive. 